1. Field of the Invention
The invention relates to impingement mixing devices and particularly to pressure control adjustments in impingement mixing devices.
2. Description of the Related Technology
Impingement mixing devices are utilized for mixing two or more components by high pressure impingement in a contained area or mixing chamber. Impingement mixing devices are particularly useful for production of polyurethane by the reaction of polyol and poly-isocyanate. Other plastic materials may also be produced in impingement mixing devices such as polyureas, nylons, polyesters, and the like. In order to achieve appropriate conditions for a reaction these components must be intimately mixed. This mixing may be achieved by high pressure impingement in a mixing head. U.S. Pat. Nos. 3,706,515 and 4,175,874, the disclosures of which are incorporated herein by reference, disclose high pressure impingement mixing heads which may be utilized in the present invention.
Prior high pressure impingement mixing heads utilize a control piston which regulates a switch over between component recirculation and component mixing phases. The high pressure mixing heads exhibit infeed ducts which contain input nozzles for introduction of the components into a mixing chamber. Input nozzles include a nozzle needle which defines an annular gap. The nozzle needle may be manually moved to set the annular nozzle gap. The setting of the nozzles sets the cross-sectional area of the inlet ports and therefore has a large effect on the impingement pressure of the components.
During production of polyurethane parts it is important that impingement pressure be controlled. Small changes in impingement pressure can have significant effects on the quality of parts produced. Disturbances factors such as differing material viscosities, nozzles needle wear, and thermal expansion of needles has an effect on the processing pressure and, thus, on the production result. In prior production processes pressure was only corrected after an operator noticed a decrease in article quality, i.e., when a large portion of produced parts were rejected.